1. Field of the Invention
The present invention relates to video signal processing circuitry, and in particular, to video signal processing circuitry within which on-screen-display (OSD) information is inserted for display.
2. Description of the Related Art
Referring to FIG. 1, as video display devices have increased in complexity and sophistication, particularly computer monitors, it is increasingly common for the display 100 in which the video image 101 is displayed to also include an OSD region, or window, 102 in which OSD information is displayed, such as one or more lines of OSD characters 103a, 103b, 103c. As can be seen, however, one difficulty that often arises is when there is little difference in color or contrast between the OSD characters and the underlying video image information. For example, as can be seen in FIG. 1, approximately the first half of the third line 103c of OSD characters is difficult, if not impossible, to read or distinguish from the underlying video image information.
Referring to FIG. 2, it has accordingly become a common practice to alter the contrast of the underlying video image information within the OSD window 102. By reducing the contrast of the background video image information 101 within the OSD window 102, the OSD characters become more readily distinguishable.
Conventional techniques for altering the contrast of the video image information 101 in coincidence with the introduction of the OSD window 102 have included implementations which add digital-to-analog converters (DACs) and analog signal mixers for altering the contrast of the video image information 101 while introducing the OSD information 103 during the OSD window 102. However, such DAC and mixer circuitry can be relatively costly and may introduce undesirable propagation delay and noise. Additionally, such circuitry generally includes a significant amount of analog circuitry which can have undesirable sensitivities to variations in fabrication processes (P), operating voltage (V) and operating temperature (T).